In general, in order to remove floating matters contained in waste water and water through coagulation and sedimentation, a chemical (coagulant) is fed into the waste water and the like to cause a coagulation reaction.
Through the coagulation reaction, a flock is formed coagulated by a coagulant such as a particle of an organic matter and a microbe or a suspended material of the waste water and the like. For the flock formation in the precipitation tank, the thickener tank, and the like, the chemical (coagulant) is fed into a pipe or the chemical (coagulant) is fed separately into the precipitation tank, the thickener tank, and the like in general
In the case of the abovementioned typical method, raw water (sludge) and the chemical (coagulant) are not agitated appropriately, and the flock is formed insufficiently, which leads to an overfeeding of the chemical during the flock formation.
In the case of a belt press dehydrator for a sludge dehydration process, an agitator of a quadrangular agitation tank at a front rotates at a slow speed to carry out agitation. In this case, sufficient time is not provided for the raw water (sludge) and the chemical (coagulant) to react with each other, and sizes of the formed flocks are irregular and large, hindering an even distribution at the belt press dehydrator.
Also, adequate agitation is unlikely while the flock stays in the agitator, which leads to the overfeeding of the chemical during the dehydration process. Therefore, a filter cloth is clogged, water filtering performance is lowered, and an increase in water content becomes unavoidable.
A centrifugal dehydrator feeds the chemical by connecting a raw water (sludge) pipe leading to the belt press dehydrator with a chemical (coagulant) pipe. A simultaneous feeding into the belt press dehydrator is made, and the flock formation and dehydration is conducted by a turning force of the centrifugal dehydrator. Since the coagulation reaction is carried out in the belt press dehydrator, the reaction is made inadequately before discharge, meaning that the water content is maintained higher than a design value during operation, and operation efficiency of the dehydrator drops due to the flock formation based on the overfeeding of the chemical.